Instead of returning an error "error doing X", just return "doing X". The
fact that it's returned as an error object says enough about that it's
an error.
This also makes it easier to chain error messages, without seeing the
word "error" in every part of the chain.
This flushes the log when the previous `Append()` call was too long ago.
Note that this doesn't flush after X seconds of silence; a call to
`Append()` or `Flush()` still has to happen in order to do the flushing.
Some parts of Flamenco had a Command consist of "name + settings", and
other parts used "type + parameters" (with the same semantics). This is
now unified to "name + parameters".
